Salinity control on Na incorporation into calcite tests of the planktonic foraminifera Trilobatus sacculifer – Evidence from culture experiments and surface sediments .

Bertlich, Jacqueline, Nürnberg, Dirk , Hathorne, Ed C. , de Nooijer, Lennart J., Mezger, Eveline M., Kienast, Markus, Nordhausen, Steffanie, Reichart, Gert-Jan, Schönfeld, Joachim and Bijma, Jelle (2018) Salinity control on Na incorporation into calcite tests of the planktonic foraminifera Trilobatus sacculifer – Evidence from culture experiments and surface sediments . Open Access Biogeosciences (BG), 15 (20). pp. 5991-6018. DOI 10.5194/bg-15-5991-2018.

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Abstract

The quantitative reconstruction of past seawater salinity has yet to be achieved and the search for a direct and independent salinity proxy is ongoing. Recent culture and field studies show a significant positive correlation of Na/Ca with salinity in benthic and planktonic foraminiferal calcite. For accurate paleoceanographic reconstructions, consistent and reliable calibrations are necessary, which are still missing. In order to assess the reliability of foraminiferal Na/Ca as a direct proxy for seawater salinity, this study presents electron microprobe Na/Ca data, measured on cultured specimens of Trilobatus sacculifer. The culture experiments were conducted over a wide salinity range of 26 to 45, while temperature was kept constant. To further understand potential controlling factors of Na incorporation, measurements were also performed on foraminifera cultured at various temperatures in the range of 19.5 °C to 29.5 °C under constant salinity conditions. Foraminiferal Na/Ca ratios positively correlate with seawater salinity (Na/Caforam = 0.97 + 0.115 ⋅ Salinity, R = 0.97, p < 0.005). Temperature on the other hand exhibits no statistically significant relationship with Na/Ca ratios indicating salinity to be the dominant factor controlling Na incorporation. The culturing results are corroborated by measurements on T. sacculifer from Caribbean and Gulf of Guinea surface sediments. In conclusion, planktonic foraminiferal Na/Ca can be applied as a reliable proxy for reconstructing sea surface salinities, albeit species-specific calibrations might be necessary.

Document Type: Article
Keywords: Salinity proxy, planktonic foraminifera, G. sacculifer, Na/Ca
Research affiliation: Dalhousie
AWI
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
NIOZ
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.5194/bg-15-5991-2018
ISSN: 1726-4170
Date Deposited: 24 Apr 2018 06:47
Last Modified: 25 Jul 2019 09:11
URI: http://oceanrep.geomar.de/id/eprint/42813

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